Synthesis of Er2Ir2O7 pyrochlore iridate by solid-state-reaction and CsCl flux method

Abstract

The solid-state reaction, hydrothermal synthesis and CsCl flux methods were employed preparing Er2Ir2O7 pyrochlore iridate. A mixture of initial Er2O3 and IrO2 oxides was thermally treated, following the temperature evolution of individual phases by means of x-ray diffraction and energy dispersive x-ray spectroscopy. Reactions by hydrothermal synthesis, using various commonly used mineralising agents, showed negligible increase in the pyrochlore phase fraction. The solid-state reaction method allowed a preparation of Er2Ir2O7, however the reacted mixture contained a high percentage (60%) of initial unreacted Er2O3. Adding an excess of IrO2 to the initial content improved the composition of the reacted sample (50% of Er2Ir2O7 for initial Er2O3:IrO2 ratio 0.9:2.1). Nevertheless, a secondary Er–Ir–O phase with slightly larger crystallographic unit cell was also created as an additional product. An optimised flux synthesis, consisting of repeated heating and regrinding cycles at 800 °C and using CsCl as a flux, provided the best conditions for single phase pyrochlore preparation. A sample with 94% Er2Ir2O7 was further improved by repeated reaction with additional excess IrO2 oxide. A successful preparation route for (at least) the heavy-rare earth pyrochlore iridates is established.